226 research outputs found
An instability of higher-dimensional rotating black holes
We present the first example of a linearized gravitational instability of an
asymptotically flat vacuum black hole. We study perturbations of a Myers-Perry
black hole with equal angular momenta in an odd number of dimensions. We find
no evidence of any instability in five or seven dimensions, but in nine
dimensions, for sufficiently rapid rotation, we find perturbations that grow
exponentially in time. The onset of instability is associated with the
appearance of time-independent perturbations which generically break all but
one of the rotational symmetries. This is interpreted as evidence for the
existence of a new 70-parameter family of black hole solutions with only a
single rotational symmetry. We also present results for the Gregory-Laflamme
instability of rotating black strings, demonstrating that rotation makes black
strings more unstable.Comment: 38 pages, 13 figure
Holography of AdS vacuum bubbles
We consider the fate of AdS vacua connected by tunneling events. A precise
holographic dual of thin-walled Coleman--de Luccia bounces is proposed in terms
of Fubini instantons in an unstable CFT. This proposal is backed by several
qualitative and quantitative checks, including the precise calculation of the
instanton action appearing in evaluating the decay rate. Big crunches manifest
themselves as time dependent processes which reach the boundary of field space
in a finite time. The infinite energy difference involved is identified on the
boundary and highlights the ill-defined nature of the bulk setup. We propose a
qualitative scenario in which the crunch is resolved by stabilizing the CFT, so
that all attempts at crunching always end up shielded from the boundary by the
formation of black hole horizons. In all these well defined bulk processes the
configurations have the same asymptotics and are finite energy excitations.Comment: version submitted to journal. Note added referring to previous work
on holographic instantons
Moving forward during major goal blockage: situational goal adjustment in women facing infertility
Individuals confronting chronic medical conditions often face profound challenges to cherished life goals. The primary aim of this study was to examine the associations of goal adjustment with psychological adjustment in the context of infertility. At study entry (T1; n = 97) and 6 months later (T2; n = 47), women in fertility treatment completed measures of goal blockage, goal adjustment ability, and psychological adjustment. At T1, greater perceived and actual goal blockage were related to negative psychological adjustment. Ability to disengage from the goal of biological parenthood was associated with less infertility-specific thought intrusion, whereas engagement with other goals was related to fewer depressive symptoms and greater positive states of mind. Greater general goal engagement was protective against the negative relationships between low goal disengagement and the dependent variables. Promoting letting go of the unattainable and investing in the possible may be a useful intervention to foster well-being among individuals experiencing profound goal blockage
Mass and Angular Momentum in General Relativity
We present an introduction to mass and angular momentum in General
Relativity. After briefly reviewing energy-momentum for matter fields, first in
the flat Minkowski case (Special Relativity) and then in curved spacetimes with
or without symmetries, we focus on the discussion of energy-momentum for the
gravitational field. We illustrate the difficulties rooted in the Equivalence
Principle for defining a local energy-momentum density for the gravitational
field. This leads to the understanding of gravitational energy-momentum and
angular momentum as non-local observables that make sense, at best, for
extended domains of spacetime. After introducing Komar quantities associated
with spacetime symmetries, it is shown how total energy-momentum can be
unambiguously defined for isolated systems, providing fundamental tests for the
internal consistency of General Relativity as well as setting the conceptual
basis for the understanding of energy loss by gravitational radiation. Finally,
several attempts to formulate quasi-local notions of mass and angular momentum
associated with extended but finite spacetime domains are presented, together
with some illustrations of the relations between total and quasi-local
quantities in the particular context of black hole spacetimes. This article is
not intended to be a rigorous and exhaustive review of the subject, but rather
an invitation to the topic for non-experts. In this sense we follow essentially
the expositions in Szabados 2004, Gourgoulhon 2007, Poisson 2004 and Wald 84,
and refer the reader interested in further developments to the existing
literature, in particular to the excellent and comprehensive review by Szabados
(2004).Comment: 41 pages. Notes based on the lecture given at the C.N.R.S. "School on
Mass" (June 2008) in Orleans, France. To appear as proceedings in the book
"Mass and Motion in General Relativity", eds. L. Blanchet, A. Spallicci and
B. Whiting. Some comments and references added
Impact of spouse caregiving on health behaviors and physical and mental health status
The impact of caring for a spouse with a progressive dementia on caregiver's health behaviors and health status was examined. Data collected from 44 spouse caregivers indicates that: • Providing full-time care interferes with preventive health behaviors (eating nutritiously, exercising) and contributes to high risk behaviors (overeating, alcohol and substance use); • Health behaviors are frequently used as coping strategies; • Caregivers rated their own health as poorer than their spouse's health; and • Disabling (arthritis, cardiac and back problems) and stress-related health problems (migraines, colitis) are a consequence of and interfere with care provision.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68204/2/10.1177_153331759400900105.pd
Assessment of insulin resistance by a 13C glucose breath test: a new tool for early diagnosis and follow-up of high-risk patients
<p>Abstract</p> <p>Background/Aims</p> <p>Insulin resistance (IR) plays an important role in the pathogenesis of diabetes and non-alcoholic fatty liver disease (NAFLD). Current methods for insulin resistance detection are cumbersome, or not sensitive enough for early detection and follow-up. The BreathID<sup>® </sup>system can continuously analyse breath samples in real-time at the point-of-care. Here we determined the efficacy of the BreathID<sup>® </sup>using the <sup>13</sup>C-Glucose breath test (GBT) for evaluation of insulin resistance.</p> <p>Methods</p> <p>Twenty healthy volunteers were orally administered 75 mg of <sup>13</sup>C-glucose 1-<sup>13</sup>C. An oral glucose tolerance test (OGTT) was performed immediately; followed by serum glucose and insulin level determinations using GBT. GBT and OGTT were repeated following exercise, which alters insulin resistance levels.</p> <p>Results</p> <p>Within-subject correlations of GBT parameters with serum glucose and serum insulin levels were high. Before and after exercise, between-subjects correlations were high between the relative insulin levels and the % dose recoveries at 90 min (PDR 90), and the cumulative PDRs at 60 min (CPDR 60). Pairwise correlations were identified between pre-exercise Homeostasis Model Assessment (HOMA) IR at 90 min and PDR 90; HOMA B (for beta cell function) 120 and CPDR 30; HOMA IR 60 and peak time post-exercise; and HOMA B 150 with PDR 150.</p> <p>Conclusions</p> <p>The non-invasive real-time BreathID<sup>® </sup>GBT reliably assesses changes in liver glucose metabolism, and the degree of insulin resistance. It may serve as a non-invasive tool for early diagnosis and follow up of patients in high-risk groups.</p
G Protein Subunit Dissociation and Translocation Regulate Cellular Response to Receptor Stimulation
We examined the role of G proteins in modulating the response of living cells to receptor activation. The response of an effector, phospholipase C-β to M3 muscarinic receptor activation was measured using sensors that detect the generation of inositol triphosphate or diacylglycerol. The recently discovered translocation of Gβγ from plasma membrane to endomembranes on receptor activation attenuated this response. A FRET based G protein sensor suggested that in contrast to translocating Gβγ, non-translocating Gβγ subunits do not dissociate from the αq subunit on receptor activation leading to prolonged retention of the heterotrimer state and an accentuated response. M3 receptors with tethered αq induced differential responses to receptor activation in cells with or without an endogenous translocation capable γ subunit. G protein heterotrimer dissociation and βγ translocation are thus unanticipated modulators of the intensity of a cell's response to an extracellular signal
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